Signals may be defined as a physical quantity, such as sound or voltage, which vary with respect to time, space or some other variable. These signals may include information wherein the information is represented by the variations in the signal. For example, the human voice or music are signals that included information based on variations in the amplitude and frequency of sound waves. It is often useful to convert a signal such as a human voice or music into an electronic signal where one or more processes can then be performed on the signal. For example, sounds such as a human voice can be converted to an electronic signal in a device such as a hearing aid. In the hearing aid example, the voice of the person speaking is converted into an analog electronic signal by a device such as a microphone. Once the hearing aid has converted the sound to an analog electronic signal, the signal can be processed to amplify one or more portions of the signal, and then converted back into sound by a speaker or other output device. The processing of the signal in the hearing aid example allows the person using the hearing aid to better hear the sounds.
In the processing of electronic signals, it is often helpful or necessary to convert the analog electronic signal into a digital signal. Digital signals allow the signals to be processed by digital signal processing systems, including systems incorporating digital computers and microprocessors. In order for an analog electronic signal to be processed by a digital signal processing system, the analog electronic signal is converted to a digital signal. This can be accomplished using an analog-to-digital converter. The analog-to-digital converter takes samples of one or more characteristics of the analog electronic signal at certain time intervals, and converts each sample into a digital representation of a value or values of the one or more characteristics of the sample. A series of these samples, taken at a fast enough sampling rate, will result in a digital representation of the analog signal.
One problem faced when performing analog-to-digital signal conversion is aliasing. Aliasing occurs when frequencies not present in the original analog electronic signal could be represented by the digital representation produced by the analog-to-digital conversion. The ability of an analog-to-digital converter to remove or at least attenuate the unwanted aliasing is referred to as image rejection, and is measured in decibels.
In addition, performing analog-to-digital signal conversions using low power is desirable in various devices, for example, devices powered from batteries where battery life and time between battery recharging are important criteria.
There is a need in the art for a system and a method for converting an analog electronic signal to a digital signal having a low power requirement, being compact, and yet being capable of operating over the required frequency range while achieving the required amount of image rejection.